Entanglement by Path Identity

Abstract

Quantum entanglement is one of the most prominent features of quantum mechanics and forms the basis of quantum information technologies. Here we present a novel method for the creation of quantum entanglement in multipartite and high-dimensional systems. The two ingredients are (i) superposition of photon pairs with different origins and (ii) aligning photons such that their paths are identical. We explain the experimentally feasible creation of various classes of multiphoton entanglement encoded in polarization as well as in high-dimensional Hilbert spaces-starting only from nonentangled photon pairs. For two photons, arbitrary high-dimensional entanglement can be created. The idea of generating entanglement by path identity could also apply to quantum entities other than photons. We discovered the technique by analyzing the output of a computer algorithm. This shows that computer designed quantum experiments can be inspirations for new techniques.

Quantum experiments and hypergraphs: Multiphoton sources for quantum interference, quantum computation, and quantum entanglement

“…The mostly transmitted laser beam undergoes up-conversion process (UC) for producing blue light with high efficiency [29], which are used to coherently pump two nonlinear crystals to generate correlated photon pairs with reasonable probabilities. Then the laser-generated single photon and photon pairs output paths are aligned identically (namely path identity [21]) such that one cannot determine the which-source information when observing the detectors. One can experimentally adjust the power of the infrared laser and exploit attenuators to change the photon creation probability p i , (i = 1, 2), where subscript i stands for the used photon source.…”

“…Until now, our hypergraph-experiment connection mainly exploits the recently developed technique -entanglement by path identity [21], where one cannot determine the origin of every N -fold coincidence event.…”

Entanglement, coherence, and redistribution of quantum resources in double spontaneous down-conversion processes

“…Systems of this type have been studied experimentally, both in the optical and in the microwave frequency range. To encompass all the physical realizations, we use a semiabstract, device-independent representation [13] which shows the mode b as common to two parametric processes (ab) and (bc) occurring in a parametrically device pumped at ω…”

“…In these scenarios, abrupt modifications of the boundary conditions [5] or of the speed of light in a metamaterial [6] by means of an external pump result in field excitations that can be amplified and detected. These processes give rise to two-mode squeezed microwaves which display entanglement [6] and other forms of quantum correlations [7][8][9], triggering the question of their employability as resources for quantum technologies [10][11][12][13].…”

Quantum optical measurements with undetected photons through vacuum field indistinguishability

“…This scheme is closely related to quantum eraser experiment in that it recovers the interference fringe from the signal photons by erasing “which-way” information of the idler photons 18, 19 . However, the need for coincidence detection between signal and idler photons is removed by perfect overlap of the two idler modes 20 . Optical component such as a beam splitter, neutral density filter, phase object, absorbing material or sample, placed between the two NL crystals would attenuate the degree of coherence of the two signal beams ( s 1 and s 2 ) or their second-order interference as the transmissivity amplitude decreases.…”